Radarsat

RADARSAT SATELLITE OVERVIEW
The RADARSAT-1 satellite was launched November 4, 1995 and has been providing imagery for operational monitoring services on a global basis ever since. It is equipped with a state-of-the-art Synthetic Aperture Radar (SAR) that can be steered to collect data over a 1,175 km wide area using 7 beam modes. This provides users with superb flexibility in acquiring images with a range of resolutions, incidence angles, and coverage areas and offers the following key benefits:
  • C-band synthetic aperture radar (SAR)
  • Cloud-free images of the Earth
  • Frequent revisit for monitoring and emergency response
  • Programming for emergencies and priorities
  • Near-Real Time processing of data
  • Direct downlink and onboard recorder storage capacity
  • Data calibration for change detection studies
  • 7 beam modes and 35 beam positions for a wide range of imaging options
  • Varying Resolutions (8 - 100 meters)
  • Swath Widths of 50 - 500 km
  • Incidence Angles from 10 - 59 degrees
The RADARSAT SAR instrument consists of a radar transmitter, a radar receiver and a data downlink transmitter. The radar transmitter and receiver operate through a steer able antenna that directs the transmitted energy in a narrow beam normal to the satellite track. The elevation angle and profile of the beam (beam positions) can be adjusted so that the beam intercepts the earth's surface over the desired range of incidence angles. This capability is important because image characteristics vary with the incidence angle associated with each beam. In addition, different resolution and coverage can be achieved. The beam modes are each characterized by a specific beam elevation angle and profile, as shown below.
Within each RADARSAT beam mode, a number of incidence angle positions are available. These are called beam positions. For example, Standard beam mode, which covers a 100 x 100 km area, has seven beam positions. By specifying a beam position, one of seven 100 x 100 km images within a 500 km accessible swath will be collected.
 
 
  RADARSAT-1 SAR Antenna & Beam Modes
 
 
Signal Data - image graphic and link to Processing Levels page
Single Look Complex - image graphic and link to Processing Levels page
Path Image - image graphic and link to Processing Levels page
Path Image Plus - image graphic and link to Processing Levels page
Map Image - image graphic and link to Processing Levels page
Precision Map Image - image graphic and link to Processing Levels page
Ortho-Image - image graphic and link to Processing Levels page
  Signal Data Single Look Complex Path Image Path Image Plus Map Image Precision Map Imag Ortho-Image
Fine
Standard
Wide
ScanSAR Narrow
N/A
N/A
N/A
N/A
ScanSAR Wide
N/A
N/A
N/A
N/A
Extended High
Extended Low
 
  The SAR instrument may be operated in one of two modes:
 
  1. Single Beam
  2. ScanSAR
 
  Single Beam Mode
  In Single Beam Mode operation, the beam elevation and profile are maintained constant throughout the data collection period. A beam is characterized by its:
  • nominal incidence angle
  • nominal swath width
  • nominal spatial resolution
 
  Single Beam Operational Modes
  Fine Beam
 
  • The Fine beam mode is intended for applications which require the best spatial resolution available from the RADARSAT system. The azimuth resolution is 8.4 m, with range resolution 9.1 m to 7.8 m from F1 to F5. Since the radar operates with a higher sampling rate in this mode than in any of the other beam modes, the ground swath coverage has to be reduced to a nominal 50 km in order to keep the downlink signal within its allocated bandwidth. Originally, five Fine beam positions, F1 to F5, were available to cover the far range of the swath, the incidence angle range from 37 to 47 degrees. By modifying timing parameters, 10 new positions have been added with offset ground coverage. Each original Fine beam position can either be shifted closer to or further away from Nadir. The resulting positions are denoted by either an N (Near) or F (Far). For example, F1 is now complemented by F1N and F1F.
  Standard Beam
 
  • Standard beam mode operates with any one of seven beam positions, referred to as S1 to S7. The nominal incidence angle range covered by the full set of Standard beam is from 20 degrees (at the inner edge of S1) to 49 degrees (at the outer edge of S7). The spatial resolution is 27 m in azimuth and 26 m (near) to 20 m (far) in range direction. Each individual beam covers a minimum ground swath of 100 km within the total 500 km accessibility swath of the full set of Standard beams. The nominal spatial resolution in the range direction is 26 m for S1 at near range to 20 m for S7 at far range. The azimuth resolution is the same, 27 m, for all beam positions.
  • Standard beam modes allow imaging over a wide range of incidence angles with optimum system image quality.
  Wide Beam
 
  • Wide beams are similar to the Standard beams except that the swath width achieved by this beam is 150 km rather than 100 km. As a result, only three Wide beams, W1, W2 and W3 are necessary to provide coverage of almost all of the 500 km swath range. They provide the comparable resolution as the standard beam mode although the increased ground swath coverage is obtained at the expense of a slight reduction in overall image quality. W1 and W2 are available for single beam products. W3 is used as one of the beams to form SWA product but not recommended for individual image because it contains a nadir ambiguity (narrow white vertical strip in the image).
  Extended High Beam
 
  • Six Extended High beam positions, EH1 to EH6, are available for collection of data in the 49 to 60 degree incidence angle range. Since this beam mode operates outside the optimum scan angle range of the SAR antenna, some minor degradation of image quality can be expected when compared with the Standard beam mode. Swath widths are restricted to a nominal 80 km for the inner three positions, and 70 km for the outer three positions. The operational beam positions on satellite are EH3, EH4 and EH6, which can cover the complete Extended High beam swath.
  Extended Low Beam
 
  • A single Extended Low beam position, EL1, is provided for imaging in the incidence a